Tension testing device for the upper and lower threads of lock-stitch sewing machines



Jan. 20,1953 c. R. MILLER TENSION TESTING DEVICE FOR THE UPPER AND LOWER THREADS 0F LOCK-STITCH SEWING MACHINES gvwc/whov CZaren cell? 11/ Z22 e 7 Filed Aug. 12, 1949 Patented Jan. 20, 1953 UNITED STATES PATENT OFFICE Clarence R. Miller, Peoria, Ill.

Application August 12, 1949, Serial No. 109,887

4 Claims.

This invention relates to certain new and useful improvements in tension testing devices and has special reference to a tension testing device for testing or measuring the tension of the upper and lower threads of lockstitch sewing machines. Machines of this character have an upper tensioning device adjacent to the spool of thread used for the purpose of tightening or loosening the tension on the upper thread and a lower device attached to the bobbin or shuttle used for the purpose of tightening or loosening the lower or bobbin thread tension. This is not an attachment for, or attached to, sewing machines. Neither is it used in any, whatsoever, in the actual operation of the sewing machine. Its purpose is to measure existing thread tensions of the sewing machine showing the operator whether the tensions are tight or loose, thereby directing the operator the correct procedure to adjust the thread tensions properly. When in use it is fastened to the flat leaf of the machine by means of suction cups, or to the flat top of a table adjacent to the machine.

This invention not only measures the existing thread tension of lockstitch sewing machines, but unerringly through a sensitive torsion spring control shows the exact amount of tension that all sewing machines must have in order to form a perfect lock stitch in the fabric, thus directing the operator to tighten or loosen the thread tensions as the case may be, in order to obtain the recommended thread tension in which a perfect lock stitch is obtained. Briefly, when the pull or tension of the thread is tightened or loosened to equal exactly the counter pull of the torsion spring tensioned arm at a given point on the calibrated scale of the tension testing device, then the tension is correct.

A number of devices have been provided for testing the thread tension of upper and lower threads of sewing machines so constructed as to be used with the intent of equalizing both the upper spool thread tension and the lower bobbin thread tension, so that sewing machine operators may be directed in adjusting the upper and/or lower tensions in order to equalize the tension of both upper and lower threads at the point where stitch is locked in the fabric being sewn. A number of patents have been issued upon the basis that the tensions on the upper and lower 2 threads above indicated should be equal. Among the patents for this purpose may be mentioned the patents to Adams No. 1,289,066; Hugentobler No. 1,456,596; Sturtevant No. 326,067; Larson et al. No. 2,457,245; and Messinger and Tetu No. 1,359,449. All of these relate merely to testing devices to aid the operator in making tension adjustments on the sewing machine, so that the pull of the thread tension on both upper and lower threads could be equalized with the same amount of tension at the point where the stitch is located in the fabric.

Several of the above mentioned patented test ing devices tend to operate with a minimum of accuracy as construction and method of using such device is such that testing operators could, only by coincidence, obtain the same reading on the testing device if a repeat test was made on the same sewing machine tensions, as not only the spring tensioned arm of the testing device to which the thread is attached would tend to pull the thread through the sewing machine tensions, but the element of trial and error entered through the necessity of the testing operator of setting the testing in operation by having to move the entire testing device with her hand at right angles to the sewing machine to a distance away from the sewing machine until the thread which is attached to the testing device has been voided of slack and a length of thread has been pulled through the sewing machine tension, this test being in operation only so long as the entire testing device is being moved by the operator in a direction away from the sewing machine, thus causing the tension of the sewing machine thread to act counter to, or pull against, the spring tensioned testing arm to which the thread is attached, whereby the human element of chance enters as the speed of movement of the operators arm, in causing testing device to be in operation, controls the position of tension indicator and thus making it impossible to ascertain the amount of thread pull, or tension of the sewing machine. Its use is confined to merely aiding the operator to equalize tensions, but does not assure an even look stitch. An experience of twenty-five years in the repair and adjustment of sewing machine defective stitching, has determined that the upper tension on the thread from the spool and the tensioning of the lower thread from the bobbin or shuttle should, in order to obtain even stitching, be different; the latter being less than the former.

I have now definitely established through experiments in testing the pull or tension on threads of lockstitch sewing machines in hundreds of machines of all ages and makes, that in order to maintain a uniform lock stitch on all types of fabric the tension must be the amount indicated and prescribed by the testing device. The proper tension is readily arrived at by reference to calibrated dial of tester, thereby permitting proper regulation of thread tensions for lockstitch sewing machines. amount of tension necessary on the thread of sewing machines is such that wheneither-the upper or lower thread in thesewing machine is properly attached to the spring controlled testing arm of the testing device and the testing My standard for the.

Figure 3 is an end view of the device taken from the right hand side of Figure 2, and

Figure 4 is a section of the invention taken on line i-4 of Figure 2.

In the construction of this invention there is provided a casing which consists of a front part Iii and a rear part H. These two parts are of about equal width so that when brought together on the line l2 they will form a substantially closed casing. Extending from the central part of the casing side i0 is a shaft [3 whereon is. mounted a sleeve Hi. Extending from the sleeve I4 is an arm I5-split'atits upperv end to provide a thread-gripping slot 16, this slot taper- .ing from the outer end of the arm downward so that when the thread T is forced downwardly therein .the .tighteriithe same will be gripped.

" Thisarm' i5 is preferably integral with the sleeve device put into operation, the amount of tension 7 on either of these two threads will bean amount that will exactly equal the amount of ''tension' on the testing arm of the testing device when it. isat aposition half way or exactly opposite thereading Correct on the calibrated dial of the testing device. .When-the thread tensions of the sewing machines are, so. adjusted, it will cause the testing arm of the device to stop in the "Correct..,position.

In view of the foregoing, it is the principal object of .thepresent invention to provide a novel devicefor properly. adjusting the thread tensions oi, sewing machines, whereby proper tension between the partsvof the thread between thesup plying spool and bobbinyor shuttle of the sewingmachinecan beproperly tested and adjusted through tightening or, loosening of tensions, so that proper tension pull maybe obtained respectivelyyforbothlower and upper threads. Another,object of. the invention is to provide means whereby the amateur and the professional home-sewer alike may, themselves, properly regulate .thevthread tension of their sewing machines without the delay, inconvenience, and expense involved in the necessity of calling a repairman tomake such adjustments which, in a very large majority of cases, is the basic trouble causing a defective stitch onsewing machines.

, Another object ofmy invention is to simplify tension regulation, on sewing machines used by students in home economics classes in clothing and textiles in our public schools. Teaching tension re ulationhas long been by the trial and erronmethod. .Myinvention now makes possible a simplified, method of instruction, whereby students may correctly set the thread tensions of their. sewing machines to the proper amount ofgtension according tomy standard, so that all of the sewing machines used, will have exactly the-same tension, thus assuring a uniform lock stitch on "operations of all the machines.

With the aboveand other objects in view that will become apparent as the nature of the invention is better understood,.jthe same consists in the novel form, combination and arrangement ofparts hereinaftermore fully described, shown .in the accompanying drawing, and particularly .claimed.

; In the drawing:

Figure 1 is a perspective view of the invention readyto apply to a sewing machine,

Figure 2 is a side elevation of the device with apart-of one side broken away to show the interior.

wand also'extendin from the sleeve M is an ,20"

arm H --carrying a counterweight it which tends to rotate the arm i5 in clockwise direction as --shown in"Figur-e ,2. Also on the shaft [3 there is mounted a second sleeve I9 whereto is fixed for radial extension an --arm 20. This arm has its free ends slidable in slot 2! made between the casing halves ii) and II and the arm is of spring type so that normally it tends to press against the edge of the slot as formed in the casing section ll.

In this side of the slot there is formed a pair of notches Z2 and 23, the notch 22 indicating medium adjustment used for testing lower thread and the notch 23 being for a'full adjustment used for testing the upper thread tension. One'or both of the members [0 and H carry means to provide a guide eye24, this being here shown as half on the casing side It and the other half on the casing side I I. This guide eye forms a means for directing the thread T to the tapered grip l6. Surrounding the sleeves l4 and [9' is a coiled torsional spring 25. One end of this spring,.as at 25, is hitched around the arm 20 while the other end 27 is hitched around the arm i5. The torsional spring is so arranged and of such strength that by pulling on the arm 20 in anti-clockwise direction, as shown in Figure '2, there will be a tendency to pullthe arm I5 in the same direction.

Thus when the testing device is set in operation by moving arm 29 back in an anti-clockwise direction, arm IE to which the thread from the sewing machine is attached will tend to move in a likewise. direction, pulling the thread from. the sewing machine with it through the tensionof the sewing machine, and thereby measuring the ,pull. or tension on the thread and indicating to the operator by reading on the calibrated dial of device at the-point where. thetorsion pull of arm -15 is exactly equaled by the pull or tension of thread being pulled by it through the tension of the sewing machine causing said arm i5 to stop movement. At'this point a reading will then show a tight, loose or correct condition. The operator may then tighten or loosen the thread tension on sewing machine, whichever the case may be and re-test if arm i5 stops in area on the calibrated dial other than that which is marked correct, until tension on sewing machine is adjusted to cause arm 15 to stop movement in correct area of calibrated dial of device. Keeping in mind, of course, that in measuring the tension of the upper thread of the sewing machine, arm

'20 is movedall the way back to slot 23 which will then put the correct amount of torsion pull on arm IE to correctly measure and adjust the tension of the upper thread.

And by the same token in measuring and adjusting the pull of tension of the lower or bobbin thread of sewing machine, arm l5 will be moved back to slot 22 which will apply a lesser amount of torsion pull on arm l5, thereby makingit correct for measuring and adjusting the lower thread tension. The function of the device with arm 20 locked in either slot 22 or 23 becomes apparent now, as it simplifies calibrated dial reading even though the amount of tension on the lower thread is less than it is for the upper thread.

It will also be apparent that after a test has been completed and a, re-test is necessary, that when arm 20 is released from slot 22 or 23in which it is held during operation, the arm I! to which counterweight I8 is attached will by its weight rotate in a clockwise direction, causing both arms [5 and 20 to return to the neutral or starting position as shown by dotted lines in Figure 2.

As a means for securing the device on an ordinary sewing machine, there is provided a pair of suction cups 28 carried by stems 29 projecting downwardly from the bottom of the casing. Thus, on any flat surface of the machine, such as is shown at 30, the device of the invention may be securely fastened.

In the operation of the device the thread T is led through the eye 24 and is then vertically held in the end 16 of the arm 15. When this is done the arm I5 is in the position indicated by dotted lines in Figure 2. The thread having been in this manner affixed to the arm 15, is tight between the eye 24 and upper end of this arm. From the arm [5 the thread runs to the eye of the machine take-up lever for the upper thread and for testing the lower thread runs from tester direct to the eye of the throat plate of the machine. The purpose of this invention is to so measure the tension of the threads of the sewing machine by pulling the thread through the tension of the sewing machine by means of movement of arm l5 that the existing tension may be ascertained from reading the indicator on the calibrated dial of the device, thereby directing the operator to make proper adjustment of tensions. This desired tension may be arranged in ways governed by the engagement of the arm 20 selectively in the notches 22 and 23. Under normal conditions the proper tension for the upper threads of sewing machines will be such that when arm 20 is locked in slot 23 the torsional movement of arm 15 will be caused to stop in a vertical position by the counter pull or tension of the thread attached thereto. Thus, when the pull or tension of the upper thread of the sewing machine exactly equals the amount of torsion which is exerted on arm 15 when it is at a vertical position, the thread tension then is correct for making a perfect lock stitch.

By the same token the normal conditions for the proper tension of the lower or bobbin thread is such that when arm I5 is engaged in slot 22 the torsional movement of arm l5 will be caused to stop in a vertical position by the counter pull or tension of the thread attached thereto. Thus, when the pull or tension of the lower thread of the sewing machine exactly equals the amount of torsion which is exerted on arm 15 when it is at a vertical position, the thread tension then is correct for making a perfect lock stitch.

It will be observed from an inspection of Figure 4 that the shaft l3 which is formed integral with the casing part III terminatesin spaced relation to the wall of the casing part II and a stud-13a projecting from the inner face of the casing part ll abuts the end of the shaft l3 and also'acts to retain the sleeves l4 and I9 in position on the shaft. Also, as shown in Figures 1 and 2, the front part III of the casing is segmentally cut away centrally of its upper portion to provide a slotted opening 3| and the wall part Illa. adjacent the opening 31 carries indicia 32 to indicate the degree of tension on the thread, such as being loose, tight, or correct.

From the above detailed description of the invention, it is believed that the construction, use, and operation thereof will at once be apparent, and while there is herein shown and described the preferred embodiment of the invention, it is nevertheless to be understood that minor changes may be made therein without departing from the spirit and scope of the invention as claimed.

What is claimed as new, is:

1. In a thread tension testing device for sewing machines, a casing, a shaft extending across said casing, a pair of levers mounted on said shaft for independent rotation thereon, the first of said levers having frictional thread gripping means at its free end, and spring means connecting said levers and causing rotative movement of the second of said levers to impart yieldable rotative movement of the first lever, said casing having separate slots through which the free ends of said levers project, one of said slots having notches in one edge for releasably locking the second lever selectively in adjustably tensioning positions of the spring means.

2. In a thread tension testing device for sewing machines, a casing, a shaft extending across said casing, a pair of levers mounted on said shaft for independent rotation thereon, the first of said levers having frictional thread gripping means at its free end, and a coiled torsional spring surrounding said shaft and having one end connected to the first of said levers and its other end connected to the other of said levers whereby rotative movement of the second lever effects rotative movement of the first lever, said casing having separate slots through which the free ends of said levers project, one of said slots having notches in one edge for releasably locking the second lever selectively in adjustably tensioning positions of the spring means.

3. In a thread tension testing device for sew-.

ing machines, a casing, a shaft extending across said casing, a pair of levers mounted on said shaft for independent rotation thereon, the first of said levers having frictional thread-gripping means at its free end, a spring means connecting said levers and causing rotative movement of the second of said levers to impart yieldable rotative movement of the first lever, and a guide eye fixedly mounted on said casing and guiding thread to said gripping means, said casing having separate slots through which the free ends of said levers project, one of said slots having notches in one edge for releasably locking th second lever selectively in adjustably tensioning positions of the spring means.

4. In a thread tension testing device for sewing machines, a casing, a shaft extending across said casing, a pair of levers mounted on said shaft for independent rotation thereon, the first of said levers having frictional thread-gripping means at its free end, a coiled torsional spring surrounding said shaft and having one end connected to the first of said levers and its other end' connected tor'ohenther of-said levers whereby rotaiiive'- movementiof the second 1e,ver efiects rotative movement of 'the first lever, and a guide eyafixedly' mounted on said" casing and guiding thread torsaid gripping means, said casingihaving separate slots through which the free ends of said levers project, one of said slots having notehes in one edge for releasably locking the second lever selectively in adjustably tensioning positions of the spring means. n

CLARENCE R. MIL-DER.

REFERENCES CITED The following references are of record in "the file of this-patent:

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Number Name Date "787,717 Bates Apr. 18,1905 811,367 Bransgrove Jan. 30, 1906 5 2,348,856 "'Se1vig -May 1 ,1944 2,457,245 Larson etal. Dec. 28, 1948 2,4861142 Fong Oct. 25, 1949 FoREIGN' PATENTS m Number 4 Country Date 350,590 Great Britain June 18, 1931 

